Various barcode readers have been proposed. The first type of devices are designed to read the entire barcode in a single scan. These first devices require long sensors that are expensive and are bulky. The second type of readers are optical scanner-type readers. In this case, the barcode is scanned by a light beam, the reflection of which is received by an optical sensor. In the case where the sensor remains fixed, as in U.S. Pat. No. 5,272,323, this sensor has a length similar to that of the first devices. In all the known cases, whether the sensor is fixed or configured to be movable during the scan, the scanning speed must be controlled, in particular kept constant. This complicates the reading process and restricts the applications for portable readers. Such readers are not suitable for reading a barcode moving at a speed that is not constant, as in the case of a chute or slide on an inclined plane involving acceleration.